Electromagnetic relays are well known and have found a variety of useful applications as switching devices. As shown in FIGS. 1, 2 and 3, a typical relay 12 includes a frame 14 and a coil assembly 16 mounted on the frame and having a core 18. An armature assembly 22 is resiliently mounted to the frame. At least one primary pair of electrical contacts 34, 48 is disposed between the armature assembly and frame. The armature assembly pivots on the frame and, in its initial position, is spaced from the core by a gap such that the electrical contacts do not mate.
A relay performs its switching function when the coil assembly is energized. The energized coil assembly creates a magnetic field which urges the armature assembly toward the core to decrease the gap. Upon sufficient closing of the gap the primary pair of electrical contacts will mate and thereby close a related electrical circuit. When the coil assembly is de-energized the armature assembly springs back to its initial position, the contacts separate and the circuit is opened. In addition, some electromagnetic relays include a supplemental pair of contacts 36, 50. The supplemental contacts are typically disposed between the armature assembly and frame but opposite of the primary pair of electrical contacts. The supplemental pair of contacts permit the relay to close a supplemental circuit with the armature assembly in its initial, de-energized position.
A strong magnetic field is generally a desirable feature. Upon closing the gap between the armature assembly and the core, the force generated by the magnetic field will cause the armature to bend in a manner similar to a loaded beam supported at its ends. The bending of the armature produces a wiping motion between the mating contacts rather than abutting contact. The wiping motion helps to prevent welding of the mating contacts which may occur in high current (in excess of 10 Amp) applications and extends the life of the contacts.
Increased magnetic force also reduces the occurrence of "bounce". Bounce occurs if the mating force between two electrical contacts is insufficient. Insufficient mating force causes the two contacts to rebound from each other on initial contact. Bounce results in lower reliability of the switching function of the electromagnetic relay and increased wear between the contacts.
The resilient mounting of the armature assembly is typically accomplished by the use of a helical spring 24, as shown in FIG. 1. The spring has one end mounted to the frame and the opposite end mounted to an extension 44 of the armature assembly. Tension from the spring pivots the armature assembly. The spring provides a resisting force to prevent closure of the gap between the armature assembly and core until sufficient electrical current is supplied to the coil. Additionally, the spring provides a restoring force to return the armature assembly to its initial position and open the primary circuit when the coil is de-energized. The spring force required, and therefore the size of the spring, is directly proportional to the strength of the magnetic field generated by the coil assembly.
The frame includes a side wall 28 having a shoulder 30. The armature assembly pivots on the shoulder. Frame locking extrusions 52 are disposed on the side wall. The armature assembly includes cut-outs 54 configured to engage the frame locking extrusions. The frame locking extrusions engage the cut-outs to prevent lateral movement of the armature assembly. Excessive movement may create a misalignment of the electrical contacts. As the electromagnetic relay is used, however, the armature assembly will slide in the direction indicated by arrow 56. As a result, contact may occur between the surfaces 58 of the frame locking extrusions and the surfaces 60 of the cut-outs. Eventually, this contact may cause the armature assembly to bind up on the frame. Binding reduces the useful life of the electromagnetic relay.
An alternate type of electromagnetic relay which addresses the problem of binding contact between the armature assembly and the frame is the blade-type electromagnetic relay. This type of electromagnetic relay utilizes a copper blade element which functions both as an armature assembly and as a spring. The blade element is mounted directly to the frame, typically by welding one end of the blade element to a side wall of the frame. The blade element curves around a shoulder of the frame, with the curvature of the element biasing the element away from the core. In this arrangement, the pivot point for the armature assembly is within the blade element and there is no pivoting contact between the armature assembly and the frame.
While the blade type relay solves the problem of wear and relative movement between the armature and frame, there are several limitations to its use. First, the blade type spring is limited to lower spring forces as compared to conventional helical springs used in comparable sized relays. The lower restoring force increases the wear of the electrical contacts and increases the possibility of bounce occurring. Second, the blade type springs are also limited to lower temperature applications due to annealing of the copper blade elements at temperatures encountered by the electromagnetic relays during automotive use. This results in limiting the blade type electromagnetic relay to lower temperature and lower current applications than the helical spring type electromagnetic relay. The third and most significant limitation is the difficulty and expense of manufacturing the blade type electromagnetic relays. The difficulty and expense are caused by the requirement for precise positioning of the blade element during attachment to the frame. This precision is necessary to ensure proper alignment of the contacts.
The above art notwithstanding, scientists and engineers under the direction of Applicant's Assignee are working to develop electromagnetic relays with increased useful lives for utilization in high current, high temperature applications.